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CHAPTER-1

INTRODUCTION : NANOCOMPOSITES OF POLYANILINE AND

MONTMORILLONITE

1.1 Composites

Composite materials are defined as materials consisting of two or more components

with different properties and distinct boundaries between them. Wood is a natural

composite of cellulose fibres in a matrix of lignin. The most primitive manmade

composite materials were straw and mud combined to form bricks for building

construction. The majority of composite materials use two constituents: a binder or

matrix and a reinforcement. The reinforcement is stronger and stiffer, forming a sort of

backbone, while the matrix keeps the reinforcement in a set place. The binder also

protects the reinforcement, which may be brittle, as in the case of the long glass fibers

used in conjunction with plastics to make fiberglass. Thus composite materials are solid

multiphase materials formed through the combination of materials with different

structural, physical and chemical properties. Composites are widely used in such

diverse applications as transportation, construction and consumer products.1

1.1.1 History of composite materials

The idea of combining several components to produce a new material with new

properties that are not attainable with individual components is not of recent origin.2, 3

Humans have been creating composite materials to build stronger and lighter objects for

thousands of years. The first use of composite dates back to the 1500 B.C. when early

egyptian and mesopotamian settlers used a mixture of mud and straw to create strong

and durable buildings. Straw continued to provide reinforcement to ancient composite

products including pottery and boats. Later, in 1200 A.D. the Mongols invented the first

composite bow. Using a combination of wood, bone, and “animal glue,” bows were

pressed and wrapped with birch bark. These bows were extremely powerful and

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extremely accurate. Composite mongolian bows provided Genghis Khan with military

dominance, and because of the composite technology, this weapon was the most

powerful weapon on earth until the invention of gunpowder. Although composite

materials had been known in various forms throughout the history of mankind, the

history of modern composites probably began in 1937 when salesmen from the Owens

Corning fiberglass company began to sell fiberglass to interested parties around the

United States. Fiberglass had been made, almost by accident in 1930, when an engineer

became intrigued by a fiber that was formed during the process of applying lettering to

a glass milk bottle.

1.1.2 Advantages

Generally, composite materials have excellent compressibility combined with good

tensile strength, making them versatile in a wide range of situations. Composite

materials take advantage of the different strengths and abilities of different materials.

They offer unusual combinations of properties of component materials such as weight,

strength, stiffness, permeability, biodegradability, electrical, and optical properties that

is difficult to attain separately by individual components. A composite material can be

custom tailored to have specific properties that will meet special requirements. They

have a longer life expectancy than steel or aluminium.The presence of combination of

properties in composite materials has led to the widespread application in many

different industries. Some important advantages of using composite materials include

● Light weight : composites are lighter in weight, compared to most woods and

metals. The lightness of composites is important in automobiles and aircraft,

because less weight means better fuel efficiency. A composite structure will

weigh ¼th of a steel structure with the same strength. A car made from

composites can weigh ¼th of a car made from steel. This equates to serious fuel

savings.

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● High strength : composites can be designed to be far stronger than aluminium or

steel. They are less likely than metals to break up completely under stress. A

small crack in a piece of metal can spread very rapidly with very serious

consequences. The fibres in a composite act to block the widening of any small

crack and to spread the stress around.

● Strength related to weight : composite materials can be designed to be both

strong and light. For this property they are used to build airplanes which need a

very high strength material at the lowest possible weight. Thus composites can

be strong without being heavy. This is because of their high strength-to-weight

ratio.

● Corrosion resistance : the right mix of constituent materials often results in

composites which are corrosion resistant. They can resists damage from weather

and harsh chemicals.

● High impact strength : composites can be made to absorb impacts like sudden

force of a bullet or blast from an explosion. Because of this property, they are

used in bulletproof vests and panels and also to shield airplanes, buildings from

explosions.

● Design flexibility : composites can be molded into complicated shapes more

easily than most other materials. Recreational boats are built from fiberglass

composites because these materials could easily be molded into complex shapes

● Nonconductive and nonmagnetic : nonconductive composites find their use in

electrical utility poles and circuit boards in electronics. The nonmagnetic

composites are also used around sensitive electronic equipment.

● Durable : composites are durable and needs little maintenance.

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1.1.3 Applications of composite materials

Use of composite materials has come a long way from mixing mud and straw to make

bricks for primitive houses. Now the composite materials are used in such diverse

applications as in home construction, aviation, ship building, car and boats, bridge

repair, diesel engines and even in ballistics protections. A few applications are

discussed here.

In construction, concrete is a complex composite of stone mixed with cement. In the

aerospace industry, many jets and airplanes are made of composite materials that are

stronger and lighter than the materials they were made from. The new Boeing 787

Dreamliner, for example, is using 50 percent composite materials dropping its overall

weight by 12 percent. Fiberglass, made of glass fibers held together by resins, was one

of the earliest composites of the modern age. Most cars today have fiberglass bumpers

covering a steel frame and are used over wheel wells and other cosmetic parts of a car

or truck. Fiberglass has become the standard material in recreational boats, from stern to

bow. Fiberglass could also be used in insulation to heat and sound absorption when

strands of fiber are interwoven with glass "wool." Its versatility allows it to be used for

home and building insulation, automobile engine compartments, ship and air

conditioning units. Composite materials are also used in bridge repairing. Graphite

epoxy, a strong and lightweight carbon-reinforced polymer capable of withstanding

heavy loads, have been used to reinforce bridge beams which increases load capacity

from 30 to 65 percent. Yet another application of composite material is in ballistics

protection for lightweight vehicles. Composite armor uses materials of varying hardness

and elasticity for heat and shock absorption.

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1.2 Nanocomposites

1.2.1 Definition

Nanocomposites are generally defined as composites in which one of the components

have at least one dimension (i.e., length, width or thickness) in the size range of 1-100

nm. Nanocomposites differ from traditional composites in the sense that interesting

properties can result from the complex interaction of the nanostructured heterogeneous

phases. In addition, nanoscopic particles of a material differ greatly in the analogous

properties from a macroscopic sample of the same material.4-6 The study of

nanocomposite materials is a fast growing area of research. This rapidly expanding field

is generating many exciting new high-performance materials with novel properties. The

properties of nanocomposite materials depend not only on the properties of their

individual parents, but also on their morphology and interfacial characteristics. There is

also the possibility of new properties which are unknown in the parent constituent

materials.

1.2.2 History

Nature has mastered the use of nanocomposites, and the men, as usual, are learning

from their natural surroundings. Although the term nanocomposite represents a new and

exciting field in material science and technology, the nanocomposites have actually

been there in the world of nature. Using carbohydrates, lipids and proteins, nature

makes strong nanocomposites such as bones, shells and wood.7 In the early 1990s,

Toyota Central Research Laboratories in Japan reported a work on a Nylon-6

nanocomposite 8, in which a very small amount of nano filler loading resulted in a

pronounced improvement of thermal and mechanical properties of nylon-6.

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1.2.3 Types of components used in nanocomposites

Based on the nature of matrix phase nanocomposites can be divided into polymeric,

ceramic and metallic nanocomposites. Usually the filler phase is embedded to the host

matrix phase to make a nanocomposite which has properties far from either phase alone.

● Polymer-matrix nanocomposites

In the simplest case, appropriately added nanoparticulates to a polymer matrix can

enhance its performance, often in a very dramatic way.9 The enhanced properties of

high performance nanocomposites may be mainly due to the high aspect ratio and/or the

high surface area of the fillers 8 since nanoparticulates have extremely high surface area

to volume ratios when good dispersion is achieved.

● Ceramic-matrix nanocomposites

In this group of composites the main part of the volume is occupied by a ceramic, i.e. a

chemical compound from the group of oxides, nitrides, borides, silicides etc. In most

cases, ceramic-matrix nanocomposites encompass a metal as the second component.

Nanocomposites from these combinations have demonstrated improvement in their

optical, electrical and magnetic properties 10 as well as tribological, corrosion-resistance

and other protective properties.11

● Metal-matrix nanocomposites

Metal matrix nanocomposites can also be defined as reinforced metal matrix

composites. One of the important nanocomposites of this class is carbon nanotube metal

matrix composite which is an emerging new material that is being developed to take

advantage of the high tensile strength and electrical conductivity of carbon nanotube

materials. In addition to carbon nanotube metal matrix composites, boron nitride

reinforced metal matrix composites and carbon nitride metal matrix composites are the

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two new metal matrix nanocomposites.12 Another kind of nanocomposite is the

energetic nanocomposite, generally as a hybrid sol–gel with a silica base, which, when

combined with metal oxides and nano-scale aluminium powder, can form superthermite

materials.13-15

1.2.4 Clay as a component of nanocomposites

Polymer-matrix nanocomposites, have been developed with diverse fillers such as

layered metal phosphates16, metal oxides17, zeolites18, mesoporous materials and

clays.19 Clays have become the most used fillers, because of their great ability to

accommodate guest species.20 Nano silicate layers lead to nanocomposite with

important tensile strength and modulus, reduced gas permeability and decreased thermal

expansion coefficient in comparision to micro and macro composite counterparts and

pure polymer matrix. This is because of the high aspect ratio of silicate layers and large

surface area available for contact with the matrix polymer.

There are different types of clays, but montmorillonites (MMT) are the most employed

in the synthesis of nanocomposites. Among all the potential nanocomposite precursors,

those based on clay and layered silicates have been most widely investigated, probably

because the starting clay materials are easily available and because their intercalation

chemistry has been studied for a long time.21 There are various reports in literature of

using clay as an inorganic filler in the synthesis of nanocomposites.22-25 Yao et al.

26

synthesized nanocomposite of polyurethane with MMT using modified 4,4′-

diphenylmethyle diisocyanate (MDI), modified polyethylene polyol (MPP) and Na+-

montmorillonite and studied the thermal conductivity. Polymer-MMT nanocomposites

based on poly (3, 4-ethylenedioxythiophene)/polystyrene sulphonate (PEDOT)/(PSS)

and montmorillonite were synthesized and characterized by Ahmad et al.24 Synthesis

and characterization of nanocomposites of MMT with poly(methyl methacrylate)

(PMMA) has been reported by Lerari et al.23 Epoxy-MMT nanocomposites were

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synthesized and the exfoliation of MMT was studied by Park et al.27 using

organically modified MMT. Mallikarjuna et al.25 used in situ melt polycondensation

method to prepare polycarbonate/MMT nanocomposites.

1.3 Clay minerals

1.3.1 Definition of clay

The term clay implies a natural, earthy, fine grained material which is composed of

largely hydrous aluminium and magnesium silicates and which develops plasticity when

mixed with a limited amount of water. Clay is referred to a part of soil fraction with the

particle size of less than 2 µm. The 2-µm grain size is the upper limit for clay minerals.

The clay layers have a thickness of about 1 nm which is in the nanoscale. The layered

silicates contain continuous two-dimensional tetrahedral sheets where individual

tetrahedra are linked with each other by sharing three basal oxygen atoms. The fourth

oxygen points in a direction normal to the sheet and simultaneously links an adjacent

alumina octahedral sheet in which the individual octahedra are bound by lateral sharing

of octahedral edges. This is shown in figure 1.1

There are many members of clays with some difference in their formula, structure and

properties including swelling and exfoliation. Those members which are able to be

exfoliated by polymer chains or monomers and distributed as individual clay layers

within polymer matrix are suitable for the preparation of polymer nanocomposites. The

individual clay layers can cause dramatic improvements in polymer properties due to

their high aspect ratio and high interfacial interactions with polymer matrix.

1.3.2 Classification of Clay

Classification of clays is based on the number of Si-tetrahedra bound to Al-octahedra in

their structures. One of the main group of clay minerals, 1:1 types are formed by

linking one tetrahedral sheet with one octahedral sheet. It is known as kaolin group with

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Figure 1.1 Representation of the structure of montmorillonites (MMT).

the general composition of Al2Si2O5(OH)5 and the layer thickness of ~ 0.7 nm. The

crystal lattice consisting of one octahedral sheet sandwiched between two tetrahedral

sheets (2:1) with the total thickness of 0.94 nm is well known as phyllosilicate. The 2:1

phyllosilicate layers can be electrostatically neutral with no inter layer ion present, and

such phyllosilicate are known as pyrophyllite. Due to absence of inter layer ions, the

layers do not expand in water. When silicon in tetrahedral sheets is substituted by

aluminum, the 2:1 structure is called mica. The negative charge induced by this

substitution is balanced by the insertion of potassium cations between layers. Due to the

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equal size of potassium cation and the hole created by Si/Al tetrahedral sheets, the

presence of potassium cation does not result in creation of inter layer spacing.

Consequently the 2:1 layers are held together strongly and the swelling or exfoliation of

layers is not possible. When in neutral pyrophyllite, the aluminum cations in the

octahedral layers are partially substituted by divalent magnesium or iron cations the

smectite clay group is formed. The negative charge created by this substitution is

balanced by inter layer sodium or calcium counter ions. The charge created on the

layers is not locally constant and varies from layer to layer. An average charge value is

considered for the layers which can be determined by cation exchange capacity (CEC)

measurement. In 2:1:1 clays, two negatively charged 2:1 layers sandwich a positively

charged brucite layer. Some examples of these three classes are given in table 1.1

1.3.3 Structure of clay

Clays have layered structure. The layers are built from tetrahedral sheets in which a

silicon atom is surrounded by four oxygen atoms and octahedral sheets in which a metal

like aluminium or magnesium is surrounded by eight oxygen atoms. The tetrahedral (T)

and octahedral (O) sheets are fused together by sharing the oxygen atoms. Unshared

oxygen atoms are present in hydroxyl form. Two tetrahedral and one octahedral sheets

fused together make the one layer structure of clay. Due to the unequal size of inter

layer cations with the holes of tetrahedral sheets, the presence of inter layer cations

causes to an inter layer spacing. The layers stay together with a regular gap between

them. The gap is called as inter layer space or gallery. The thickness of the repeated

units in a regular multilayer structure and one inter layer space is called d-spacing or

basal spacing (figure 1.1). The basal spacing of clays can be measured or calculated

from their X-ray diffraction patterns. The inter layer dimension is also dependent to the

nature of clay and swelling or degree of hydration of inter layer cations. Due to the inter

layer spacing and weak forces between layers, especially in the hydrated form, other

molecules also could be intercalated between layers. This leads to the expansion of

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layered lattice and finally may cause the separation of individual layers. The unique

intercalation/exfoliation behavior of smectite clay minerals makes them very important

and powerful as reinforcing fillers for polymers.

Table 1.1 Classification of clay minerals

Type Name of the group Charge/formula unit Common

species

1:1 Kaolinite and Serpentine 0 Kaolinite

Halloysite

Chrysotile

2:1 Micas

Vermiculite

Smectites

Pyrophyllite and Talc

≤ 2

1.2 – 1.8

0.2 – 0.6

0

Illite

Vermiculite

Montmorillonite

Beidellite

Nontronite

Saponite

Pyrophyllite

Talc

2:1:1 Chlorite 1.1 – 3.3 Donbassite

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1.3.4 Cation exchange capacity (CEC)

Cation exchange capacity (CEC) of a clay mineral is the quantity of cations reversibly

adsorbed per unit weight of the clay mineral. CEC is expressed in mili-equivalents per

gram or more commonly per 100 gm of clay ( meq/100g).

In clay minerals, Si+4 is sometimes replaced by Al+3 in tetrahedral sheets and Al+3 is

replaced by Mg+2 in octahedral sheet. This results in the unbalanced charges in the

structural units of the clay minerals. These substitutions are mainly balanced by

adsorbed cations. So, cation exchange capacity results from substitution in octahedral

and tetrahedral sheets of clay mineral. The predominant substituents are Mg+2 and Fe+3

for Al+3 in the octahedral sheet. Al+3 may also be substituted for Si+4 in the tetrahedral

sheet. This gives rise to charge deficiency which varies depending on the degree of

substitution. These charges are sometimes balanced by other lattice arrangements e.g.

replacing OH for O or by filling more than two thirds of the possible octahedral

positions. But commonly, these charges are balanced by external alkali (Na) or alkaline

earth metal (Ca) ions. These cations are found to be mostly on basal cleavage surfaces

of the clay minerals. In most of the clay minerals the CEC results from substitution in

the octahedral sheet. When the substitution is in the tetrahedral sheet the exchangeable

ion are held more strongly than the substitution in the octahedral sheet. Incorporation of

guest species into the clay interlayer is depicted by the term intercalation or

intersalation. When a cationic species is exchanged into the interlayer of a clay upto the

CEC it is termed intercalation and when the exchange is excess over the CEC it is

termed intersalation.

1.3.5 Swelling of Smectite Clay (MMT)

Because of the inter layer spacing and weak inter layer forces, the cations present

between the layer can be hydrated in aqueous solutions. This is known as clay swelling.

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The swelling causes the increase of inter layer spacing. The charge density on the clay

layers is different in various clay groups with different clay structures.28 Swelling is

one of the most prominent properties of smectite clay. Smectite clays possess a

combination of cation exchange, intercalation and swelling properties which make them

unique. Swelling is the ability to expand beyond a single molecular layer of intercalant.

Extent of swelling depends on the polarity of the swelling agent, the interlayer cations,

the layer charge and the location of the charge.

Figure 1.2 Swelling of smectite clay in presence of water.

When water penetrates the interlayer forming one to four monolayers, the volume of the

dry clay just doubles, and this swelling is termed as interlayer or intracrystalline

swelling. When the water uptake goes beyond this, and a spectacular swelling occurs

along with water adsorption on external surfaces and pores, it is called osmotic or

intercrystalline swelling. Schematic representation of swelling of smectite clay in

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presence of water is shown in figure 1.2. The increase in interlayer spacing that occurs

with swelling of MMT clay in water is large and enables it to be penetrated by relatively

large size molecules. The polarizing power and the polarity of the interlayer cations

influence the swelling nature as well as the basal spacing of the clay. Thus at 52%

relative humidity, basal spacing of Na-MMT, NH4-MMT and Ca-MMT are 12.5, 11.7

and 15.1Å respectively 29 due to the difference in polarizing power of the interlayer

cations in the same solvent. Basal spacing of Na-MMT is 16.9 – 17.1 Å for ethylene

glycol, 17.8 Å for glycerol and indefinite for water 29, 30 because of the difference in

polarity of the swelling agents.

1.3.6 Modification of Clay

In their pristine state layered silicates are only miscible with hydrophilic polymers, such

as poly(ethylene oxide) and poly(vinyl alcohol). In order to render them miscible with

organophilic polymers, one must exchange the alkali counter-ions with a cationic-

organic surfactant. Alkylammonium ions are mostly used, although other “onium” salts

such as sulfonium and phosphonium 31, 32 could also be used.. This could be readily

achieved through ion-exchange reactions that render the clay organophilic 33. In order to

obtain the exchange of the onium ions with the cations in the galleries, water swelling

of the silicate is needed. For this reason alkali cations are preferred in the galleries

because 2-valent and higher valent cations prevent swelling by water. The hydrate

formation of monovalent intergallery cations is the driving force for water swelling.31

Natural clays may contain divalent cations such as calcium and require exchange

procedures with sodium prior to further treatment with onium salts.33 The alkali cations,

as they are not structural, can be easily replaced by other positively charged atoms or

molecules, and thus are called exchangeable cations.34

In addition to the surface modification and increasing the hydrophobicity of clay layers,

the insertion of alkylammonium or alkylphosphonium cations into the galleries causes

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to some degree of increasing in the inter layer spacing which promotes intercalation of

polymer chains into the galleries during nanocomposite preparation.35 Figure 1.3

schematically shows the modification of clay layers using alkylammonium cations via

the ion exchange process.

There are several methods for modification of clay. Modification simply means

replacement of exchangeable cations of the clay. When the inorganic ions of the clay

surfaces are replaced by quarternary ammonium cations such as tetramethyl ammonium

(TMA), cetyl trimethyl ammonium (CTA), tetraethyl ammonium (TEA),

benzyltrimethyl ammonium (BTMA), or polar organic compounds then the clay is said

to be organically modified. Modification of the clay in this way imparts organophilic

character to the clay. Clays are also modified by treating it with acids such as HCl or

H2SO4 in which case exchangeable cations of the clay are replaced by H+ leaching Al+3

and other cations from both tetrahedral and octahedral sites. Other modification

methods includes treatment of the clay with metal nanoparticle, metal complex in which

case the metal ions or metal complex are exchanged into interlamellar space of layered

clay minerals depending upon the CEC of the clay.

1.3.7 Montmorillonite (MMT)

Among the large number of layered solids such as graphite, layered double hydroxides,

transition metal dichalcogenides, metal phosphates and metal phosphonates, clay

minerals especially the members of smectite group are the most suitable candidates for

synthesis of polymer nanocomposites,because they possess a unique structure and

reactivity together with high strength, stiffness and high aspect ratio of each platelet. In

particular, montmorillonite,[Mx(Alx-2Mgx)Si4O10(OH)2.nH2O] where M indicates

exchangeable monovalent ions, is most widely used in this field. Montmorillonite is a

hydrophilic mineral and belongs to the general family of 2:1 phyllosilicates, being

composed of stacked layers of aluminium octahedron and silicon tetrahedrons.

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Substitution of aluminium with magnesium in MMT will create an overall negative

charge which is compensated by exchangeable metal cations such as Na+, K+, Ca+2,

Mg+2. 36

Figure 1.3 Modification of clay layers by alkylammonium ions

1.3.8 Advantages of clay as a constituent of composite

Clays among other hosts are natural, abundant and inexpensive mineral that have

unique layered structure, high mechanical strength as well as high chemical resistance.

Adoption of clay (MMT) to the field of nanocomposites lies in its small particle size

(<10 µm), ease of intercalation, easy hydration and capability to contain various

organic/inorganic materials.37 Their lamellar elements display high in-plane-strength,

stiffness as well as high aspect ratio.38 MMT layers have the capability to impose better

arrangement of the polymeric chains.39 Such new materials often exhibit physical

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properties superior to those of macro-scale composites, making their technological

application attractive.

1.4 Conducting polymers and Polyaniline

Conducting polymers are a class of polymer with conjugated double bonds in their

backbones. They display unusually high electrical conductivity and become highly

conductive only in their doped state. Due to the excellent electrical and electronic

properties and plastic nature of conducting polymers, they have been proposed for

applications such as antistatic coating, corrosion protection, electrochromic display,

sensors, light-emitting diodes, capacitors, light weight batteries and gas permeation

membranes etc. They are also believed to be promising alternatives to the

environmentally hazardous chromate based conventional coatings.

Unlike traditional polymers, which are electrical insulators, conducting polymers (CPs)

are semiconducting and can be doped into regions of metallic conductivity. 40-43 This

novel finding, at odds with what had been previously expected of polymers, yielded the

2000 Nobel Prize in Chemistry for Alan J. Heeger, Alan G. MacDiarmid and Kideki

Shirakawa for the discovery and subsequent development of this new class of

materials.Thanks to intense research efforts, there are now a large variety of CPs, with

polyacetylene, polythiophene, polypyrrole and polyaniline (PANI) being four of the

most studied and promising types. PANI exhibits high conductivity, excellent

environmental stability, is of low-cost and straightforward to synthesize.44 It is also

unique among CPs in that it has a reversible and relatively simple acid–base doping–

dedoping pathway, useful for tuning its electrical and optical properties. By offering

metal-like electrical and optical properties in addition to the inherent ease of processing

and mechanical flexibility of polymers, innovative new devices and applications have

been made possible by CPs. Moreover, the morphology of such materials can be tuned

at the nanoscale. This nanostructuring of materials, by designing their dimensions to be

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on the order of hundreds of nanometers or lower, often yields novel properties.

Examples are improved strength and conductivity usually due to an increase in

molecular ordering, as well as improved reactivity typically due to higher surface area.

Combining these two sources of innovation, CPs and nanostructuring, has been an area

of intense study in recent years 42, 45–48 yielding innovative applications.49,50

1.5 Nanocomposites of clay and conducting polymers

The introduction of an organic guest into an inorganic host material by the intercalation

technique has resulted in the fabrication of nanocomposite materials with high potential

for advanced applications. These polymer nanocomposites consist of multilayered

sandwich-like elements in which polymer chains are sandwiched between ultrathin

sheets of an inorganic material. Such confinement of polymer molecule is expected to

lead to a high degree of polymer ordering and enhanced thermal and oxidative stability

which is hard to find in pristine polymers. Nanocomposites based on conducting

polymer 51 and different inorganic compounds are the representatives of the further

development of ideas about nanostructuring, because such nanocomposites display

novel and frequently important mechanical, electronic, magnetic, optical and catalytic

properties inaccessible in both individual components of the nanocomposites and their

micro analogues.52 ,53

Incorporation of guest electroactive polymers such as polyaniline , polypyrrole (PPy)

etc. into host clay particles has attracted great attention because of their better

processibilty with colloidal stability, mechanical strength and novel electrical, catalytic

properties.20 MMT was used to prepare nanocomposites with a number of conducting

polymers such as polyaniline, polypyrrole and copolyaniline 58 and their anti-corossion

properties were studied.54 Use of MMT in the preparation of nanocomposite with

polypyrrole has been reported by Anuar et al.59 and their intercalation behavior were

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studied.55 Polymer intercalated nanocomposites, prepared by using layered materials,

have a high degree of polymer ordering and exhibited advanced gas barrier, thermal

stability, and enhanced mechanical properties compared to pristine polymers.56 There

are a number of reports on the preparation and properties on the lamellar

nanocomposites of polyaniline with various layered materials.57-59 Recently,

conducting polymer layered inorganic solid nanocomposites have been the subject of

considerable research interest because, being derived from a unique combination of

inorganic and organic components, they have possible technological application and

raise challenging scientific issues.60 Bein et al.61, 62 and other researchers prepared

conducting polymers inside the cavities of a broad amount of natural and synthetic

zeolites. Indeed, chains of polyaniline, polypyrrole and polythiophene were

encapsulated into many forms of zeolites.63 For clays it is also possible to form PANI in

their cavities through intercalation of the protonated monomer, by cation exchange,

followed by oxidation with ammonium persulphate in aqueous suspension.63

1.6 Nanocomposites of polyaniline and MMT

The MMT clay has been extensively employed 64 in polymerization studies of aniline or

its derivates with the aim to form nanocomposites with controlled structure. The

combination of conducting polymers with host materials having different characteristics

opens a way to new hybrid materials showing novel properties. Also confinement of

polymer chains in the interlayer spaces may enable to further characterize the polymer

structure. The synthesis of polyaniline–clay nanocomposites is currently carried out by

intercalation of the monomer followed by the polymerization in the clay interlayer. Kim

and co-workers 65-67 have synthesized polyaniline–montmorillonite nanocomposite

using an emulsion intercalation method. Yang et al. 68 and Jia et al. 69 on the other hand,

have synthesized PANI–montmorillonite nanocomposites with organically modified

clays. There are several reports focusing on the design, preparation and characterization

of novel nanocomposites consisting of polyaniline and MMT.24, 65, 70-75 There are several

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other reports of synthesizing and characterizing MMT/PANI nanocomposites using

different polymerization procedures.77,78 Nascimento et al.78 synthesized PANI in

presence of MMT and obtained PANI-MMT composite by polymerization of

An+-MMT. Nayaranan et al.76 synthesized PANI-MMT nanocomposite by oxidative

polymerization using H2O2. Celik et al.79 synthesized intercalated PANI-MMT

nanocomposite with varying aniline(g)/MMT(g) ratio using benzoyl peroxide as the

oxidant. Srivastava et al.80 prepared intercalated PANI-MMT nanocomposite by

oxidative chemical polymerization with ammonium persulphate. MMT intercalated

conducting PANI has also been synthesized by Kulhankova et al.81 Zaarei et al.

56 also

synthesized PANI-MMT nanocomposite and studied the corrosion resistant properties

of the nanocomposite. Recently, Hosseini et al.82 studied the effect of PANI-MMT

nanocomposite on corrosion performance of epoxy coatings. Exfoliated PANI-MMT

nanocomposites were synthesisied by in-situ polymerization of aniline onto pre-

exfoliated transition metal ion exchanged montmorillonite clays by Nayaranan et al.22

and confirmed the exfoliation of clay layers by XRD studies.

3.7 Aim of the present work

Emulsion polymerization is an important method used for the preparation of

polyaniline-montmorillonite (PANI-MMT) nanocomposites in presence of a surfactant

and a dopant. There are reports where surfactants serve both as emulsifier and dopant.

Kim et al.65 used dodecyl benzene sulphonic acid both as surfactant and dopant for the

synthesis of PANI-MMT nanocomposites. There is however no reported work where

dodecyl sulphuric acid was used as the surfactant and dopant and the present work

describes the use of dodecyl sulphuric acid for the first time in the synthesis of

polyaniline- MMT nanocomposite. The broad objectives of the work are :

PART-B Chapter-1

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(i) To synthesise PANI-MMT nanocomposites with pristine MMT in presence of

dodecyl sulphuric acid.

(ii) To characterize PANI-MMT nanocomposites by UV-Vis, FTIR spectroscopy,

XRD, TGA and SEM studies and to determine the room temperature conductivity

of the composites.

(iii) To synthesise PANI-OMMT nanocomposites with organically modified MMT

(OMMT) in presence of dodecyl sulphuric acid.

(iv) To characterize PANI/OMMT nanocomposites by UV-Vis, FTIR spectroscopy,

XRD, TGA and SEM studies and to determine the room temperature conductivity

of the composites.